Well I have a stepsister that's 11 and lately I've been kinda uneasy around her. I mean, I don't show it but I definitely am nervous around her.
Basically, we have a older sibling (me), younger sibling (her) relationship. You know, younger sibling annoys the hell out of the older sibling and then the older sibling would say something like "Go the hell away. You're annoying as hell!" And insults yada, yada...
The thing is, I'm more of a 'I REALLY DON'T FEEL LIKE PUTTING UP WITH YOUR SHIT' type of older sibling. So of course, the insults would be more 'intense' and such.
Now this has been going on for about a year and I know she probably hates me too. My cousins would tell me that whenever she'd walk behind me, she'd mouth curse words behind my back. To be honest, I want nothing to do about her. I don't really care for her. But, her parents are divorced and her mom never gave her any true love so she'd constantly "feed" off my mom's love and act like a 5 year old around my mother (which I'm totally fine with. She has also never had an older sibling so I guess she doesn't understand the way siblings would fight and argue alot.)
Lately though, my stepsister has been acting sorta strange. Like a little demon who's trying to lure her victims into a secluded area, only to knife them and kill them. It's unnerving, I swear.
Whenever my cousins are around, she'd pull them away from me with excuses like: "Oh, Cherry, your mom's here." or "Hey, can you go get *insert item* for me?"
I'm probably being a little paranoid but this has really been bothering me for awhile. I can already see her stabbing me to death...
So do you guys think I'm being too paranoid?

I think you two should just bone and get it over with.
I mean obviously there is some tension.

Some intimate tension.

Start caring for her. Honestly, what could she have done to make you feel this way towards her. She's human just like us. There is no reason to be like that towards your younger step sister. So what if you're not blood siblings. You are still siblings.

>>3 This.

As a younger sibling, I can say that older siblings can be wayy too harsh. So what if she's annoying? One day, you're (probably) going to have a kid, and that kid is going to be just as annoying. But are you going to scream at them and insult them and then whine online that you're afraid they're going to get revenge? No, because by then you would have realized what I'm about to tell you - just because something's annoying doesn't mean you can treat it like shit. Kids younger than you will always be annoying, but that doesn't mean you can act like an ass. Be the better man and don't get involved if she tries to start a fight. Of course she's going to cuss around you and take people away from you - in her eyes, you're an asshole who hates her, and you don't deserve anything. Whether she liked you or not at the beginning doesn't matter now; she's required to hate you, the only sibling she has, and this is her payback for it.

I'm not saying that she's not equally responsible. It's just that you're the older part of this and you need to be the one to take that responsibility and fix this relationship, even if just a bit. I highly doubt she's plotting to kill you; she's just pissed off, and she'll stay pissed off until you both start to put some effort into fixing this bullshit.